Ceramic honeycomb structure for accommodating compression and tension forces

ABSTRACT

An improved ceramic honeycomb structure is provided by having a configuration with thin curved walls between the multiplicity of cells whereby both compression and tension forces can be better accommodated when the structure is being subjected to non-uniform temperature conditions. Two or more sets of opposing curved walls can be used to define each cell of the multiplicity thereof and the curvature for each set of walls is such as to permit elongative deformation in one direction without causing a reduced width cell or a closer spacing for juncture lines between adjacent cells in a direction transverse to the expansion movement.

United States Patent [191 Gerhold 51 Sept. 2, 1975 1 CERAMIC I-IONEYCOMBSTRUCTURE FOR ACCOMMODATING COMPRESSION AND TENSION FORCES [75]Inventor: Clarence G. Gerhold, Palatine, Ill.

[73] Assignee: Universal Oil Products Company, Des Plaines, 111.

[22] Filed: Sept. 20, 1973 [21] Appl, No.: 399,774

[52] US. Cl. 428/116; 23/288 FC; 156/89;

428/1 18 [51] Int. Cl. 1332B 3/12 [58] Field of Search 29/455 LM;161/68, 69;

156/89, 197; 23/288 F, 288 PC; 52/615, 618; 181/36 C, 71; 252/477 RPrimary Examiner-l-larold Ansher Assistant Examiner Henry F. EpsteinAttorney, Agent, or FirmJames R. Hoatson, Jr.; Philip T. Liggett;William H. Page, II

[5 7 ABSTRACT An improved ceramic honeycomb structure is provided byhaving a configuration with thin curved walls between the multiplicityof cells whereby both compression and tension forces can be betteraccommodated when the structure is being subjected to nonuniformtemperature conditions. Two or more sets of opposing curved walls can beused to define each cell of the multiplicity thereof and the curvaturefor each set of walls is such as to permit elongative deformation in onedirection without causing a reduced width cell or a closer spacing forjuncture lines between adjacent cells in a direction transverse to theexpansion movement.

4 Claims, 6 Drawing Figures CERAMIC HONEYCOMB STRUCTURE FORACCOMMODATING COMPRESSION AND TENSION FORCES The present inventionrelates to an improved design and arrangement for cells in a ceramichoneycomb structure such that there can be greater ability to withstandthe compression and tension forces which can result from non-uniformhigh temperature conditions, as for example, when a honeycomb section isbeing utilized as a support for an oxidizing catalyst coating.

More particularly, there are herewith provided improved forms ofhoneycomb structures by virtue of special cell configurations which haveall curved walls between common juncture lines forming the multiplicityof cells such that tension conditions can be better accommodated withoutcausing breakage of the monolith walls.

One of the serious problems in connection with the use of ceramicmonoliths or honeycomb type of structures as supports for catalystcoatings results from the fact that a catalyst structure, or even a bedof catalyst particulates, does not operate at a uniform temperaturethroughout its length or across its cross-section. There are normallysubstantial temperature differences between the inlet of the unit andthe outlet end thereof, as well as differences between the centralsection and the areas adjacent to the catalyst chamber walls. As aresult those sections of the catalyst unit which are at a highertemperature will undergo greater expansion than those at the lowertemperatures and there will also be various sections of the monolithicunit undergoing either tension or compression. Typically, the ceramiccomposites forming the conventional forms of monoliths are fairly strongin compression, at least in comparison to tensile strength, such thatthere can readily be cracks and failures in the tensioned portions of aunit because of excessive stressing.

It is realized that various honeycomb configurations, with respect tothe cross-section of cells, have been made and used for absorptionelements and for catalyst supports in the air pollution field.Individual cells of a particular honeycomb may be square, rectangular,triangular, hexagonal, round, oval, etc., as well as of different sizesand diameters. Typically, where a ceramic honeycomb is used as acatalyst support member, it will be selected to have as small cells aspossible, without creating excessive pressure drop for the fume stream,in order to provide a maximum of catalytic surface area. However, thesmaller the cells, the greater is the rigidity and there is a loweringof flexibility for a given structure.

While it is a feature of the present invention to provide for curvedinterconnecting walls to extend between juncture lines and to effect thepartitioning between adjacent parallel cells in a monolith, it must berealized that conventional circular or oval patterns for cells will notprovide the desired flexure and deformation to help overcome tensionbreaks. Also, the curved wall cell configurations resulting from node tonode contact points with the use of adjacent corrugated sheetmanufacturing procedures, such as taught in US. Pat. No. 3,444,925, donot seem to result in suitable stress relieving patterns. For example,with a pattern providing circles, or ovals, in the cross-section of ahoneycomb, there will be tensile forces without the available wallmembers to readily give and lengthen. Stated another way, with the useof curved wall patterns, from circular or oval cells, there will stillbe a tendency for juncture lines to move closer together in a directiontransverse to a tension force and there is no real elimination ofbreakage problems from non-uniform temperature conditions.

On the other hand, it may be considered a principal feature of thepresent invention to use curved members, rather than straight, toprovide cell walls and connect juncture lines between a plurality ofadjacent cells and, at the same time, have the curved walls form specialpatterns which will not tend to cause juncture lines to move closertogether in a direction generally transverse to the walls beingsubjected to lengthening and straightening from a tensile condition.

The improved form of cell configuration can be accomplished, by way ofexample, in a design where square cells would have the straight wallsreplaced by arcs in which the curvature alternates between concaveinward and convex outward to result in dumb-bell shaped cells. Also,where the walls of what would be a normal hexagonal pattern are made tobe arcuate and they alternate between being concave inwardly and convexoutwardly, then there is a resulting cloverleaf" shape for each cell.

In a broad embodiment, the present invention provides a ceramiccomposite with a multiplicity of parallel cells in a honeycomb type ofstructure which can deform to accommodate compression and tensile forcesfrom non-uniform temperature conditions, which comprises, having allinterconnecting walls between juncture lines between adjacent cellsbeing curved and oriented one to another in a reoccurring symmetricalpattern, with next adjacent walls around an individual cell alternatelybowing inwardly and outwardly, and there being at least two sets ofopposing curved walls to form each cell of said structure, wherebyexpansion movements in directions transverse to the length of thelongitudinal cells that are due to differential temperature conditionscan cause deformation and straightening of one set of opposing curvedwalls without causing juncture lines between cells to tend to movecloser together in a direction generally transverse to the walls beingstraightened and to thereby provide a less fragile structure.

In a specific embodiment, there may be a configuration which is amodification of a conventional square pattern in that each cell willhave an opposing set of partitioning walls which are concave toward oneanother and then at thereto there will be a second set of partitioningwalls which are curved outwardly, or convexly away from one another,such that the resulting configuration for each cell will be of adumb-bell shape. Also, where walls alternate between bending inwardlyand outwardly, the resulting overall pattern is such that any one cellwill have adjoining dumb-bell shaped cell configurations that are atright angles thereto. This arrangement permits tensile stress elongationin one direction by virtue of wall curvature permitting some measure ofdesired elongation without breakage while, at the same time, thereshould be substantially no narrowing of spacing with respect to juncturepoints between cells in a direction transverse to the elongation.Actually, there may be some local spreading of juncture lines due torotation thereof and to partial straightening of the transverse walls.

In another embodiment, there may be provided a curved wall modificationfor what might normally be considered a hexagonal cell pattern, withthree sets of opposing curved walls rather than three sets of straightwalls as provided in a conventional hexagon. Opposing curvedpartitioning walls between adjacent cells in any one row thereof will bebowed in the same direction and each cell in any given row of cells willhave the same cross-sectional configuration and orientation. Also inthis arrangement, the curved walls for any one cell will alternatebetween being concave inwardly and convex outwardly around the peripheryof such cell such that the result is a cell unit being generally ofclover-leaf shape. With respect to flexibility, this arrangement permitstensile forces to, in effect, straighten or elongate two sets of wallportions of a particular cell with little or no movement betweenjuncture lines in a direction transverse to the tensile forces, wherebyflexibility is in effect built into the honeycomb structure toaccommodate differential temperature conditions. The deformation andflexibility aspects will be more clearly explained and set forth inconnection with the subsequent description of the drawings.

The desired special cell configurations in a honeycomb type of structuremay be obtained during the manufacturing process by extruding theceramic material through suitably shaped die means; however, other formsof manufacture may be utilized. For example, specially shapedmodifications of a corrugated type sheet may be utilized to conform withand form a juncture with other specially formed sheet members such thatthe desired clover-leaf pattern could result in the final product. Inother words, the procedure of manufacturing honeycomb type of monolithicstructures such as set forth in US. Pat. Nos. 3,444,925 and 3,505,030might well be utilized in the present instance. Also, sheet-like membersof ceramic material in a curved or corrugated form may be slotted andsubsequently nested in the manner of making an egg-crate type of cartonto form the modified, curved wall square, configuration where the resultis the multiplicity of dumb-cell shaped cells. Where sheets ofcorrugated films of green ceramic are nested with, or made to contactadjacent sheets or panels, then during the curing or firing stage thereis a fusing and sintering of the contacting sheets to form the desiredshapes and juncture points between longitudinal cells, such as is setforth and described in the aforementioned patents.

In still another procedure, there can be the formation of a ceramicmixture around suitably shaped burnable core members and a firing andburning away of the. core material from the ceramic material to resultin de sired shaped cells for the honeycomb element. In other words, itis not intended to limit the present invention to any one method ofmaking the honeycomb ceramic structure, nor is it intended to limit theinvention to any one type of material that will form the resulting rigidcellular structure. For example, the ceramic may comprise refractorycrystalline materials such as sillimanite, magnesium silicates, zircon,petalite, spodumene, cor dierite, alumino-silicates, mullite, etc. Suchmaterials are of advantage in having relatively high porosity over theirsurface areas and being suitable for supporting catalyst coatings to, inturn, provide catalytically active conversion elements.

The present honeycomb elements may be utilized to advantage, withoutcatalyst coatings, as absorption structures or heat exchange elements;however, such types of coated structures are finding wide usage in catalytic converters adapted to have auto exhaust fumes passed thcrethroughto effect conversion and elimination of undesired components such ascarbon monoxide, hydrocarbons and nitrogen oxides. While it is notintended to limit the present invention to any one specific type ofactive catalyst coating, such coating may comprise an oxidation catalystand may include the metals of Groups I, V, VI and VIII of the PeriodicTable, particularly copper, silver, vanadium, chromium, iron, cobalt,nickel, platinum, palladium, with a component being used singly or incombination with one or more other active component. Also, typically,the ceramic honeycomb material will have been coated with a suitablerefractory inorganic oxide such as alumina or alumina combined with oneor more other refractory inorganic oxide. Typically, the oxidesupporting layer will be applied to the wall surface prior to thecoating of the active catalytic component although there may be amixture of refractory metal oxide support material with the activecatalytic component and the mixture sprayed, dipped or otherwise coatedonto the walls of the cellular structure. Although not intended to belimiting, reference may be made to US. Pat. No. 3,565,830, which setsforth various methods for coating a refractory honeycomb type of memberwith an alumina slip and an active catalytic coating.

Reference to the accompanying drawing and the following descriptionthereof will serve to illustrate variations in the flexible cell designbeing provided for a honeycomb type of ceramic structure and the meansfor forming the special cell configurations, as well as point out howdifferential temperature conditions provide failure problems withconventional ceramic honeycomb elements.

FIG. 1 of the drawing indicates diagrammatically how differentialtemperature conditions across a conventional honeycomb element cancreate tensile forces leading to breakage in cell walls of a honeycombelement.

FIGS. 2 and 3 of the drawing indicate diagrammatically two differentforms of cellular configurations which provide curved wall portions thatcan better accommodate tensile stressing from differential temperatureconditions.

FIG. 2A indicates diagrammatically how an individual cell may bedeformed and elongated without leading to immediate breakage.

FIGS. 4 and 5 indicate diagrammatically how specially formed ceramicsheet material may be joined with other specially formed sheets toprovide resulting curved wall cells.

Referring now particularly to FIG. 1 of the drawing, there is indicateda portion of reactor unit 1 having a cylindrical form wall or chamberportion 2 adapted to hold an internal honeycomb element 3. Where theunit is serving as an exhaust fume reactor to convert hydrocarboncontaining exhaust gas fumes and the cellular structure 3 iscatalytically coated with an active oxidation catalyst, there can behigh temperature conditions through the interior of the reactor of theorder of 1200 to l600 F. However, during certain stages of operation andperhaps during most operating periods, there will be a substantiallyhigher temperature in the central core portion 3' as compared to theperipheral portion of the honeycomb, being indicated as 3". The hotinterior will therefore tend to expand, from the high temperatureconditions, to a far greater degree than the peripheral section 3 and,as indicated by the arrows, the outward thrust from the expansion of theinterior material will necessarily cause resulting hoop stress ortension in the outer ring of cells 3" and lead to wall breakage. Asindicated hereinbefore, typical ceramic materials can be relativelystrong under compression conditions but will have very little strengthto accommodate tensile forces and will readily shatter and break,particularly where straight walls are being utilized for the honeycombcell configuration such as indicated in the present FIG. 1.

With reference to FIG. 2 of the drawing, there is indicated a specialcell configuration which provides curved wall portions that can, inturn, provide flexure to a resulting honeycomb element. Specifically,there is indicated a curved wall modification for what might beconsidered a normally square pattern or layout such as indicated by thedashed lines 4. In particular, the present pattern is provided by havingall arced or curved walls for each and every cell of the entirehoneycomb structure with the curved walls alternating around aparticular cell from being curved inwardly to being curved outwardly.With reference to a particular cell such as C, it will be noted thatthere are opposing walls 5 which are concave toward one another while atright angles thereto there are opposing walls 6 that are convexoutwardly to bow away from one another. The net result is a dumb-belltype of shape for the cell C by virtue of the necked-in portion in thecentral zone. It will also be noted that the pattern for C is repeatedat every other location in any one row. It may also be noted that eachnext adjacent, or touching, cell c has the same dumb-bell configurationbut is at right angles to C in orientation.

In order to further illustrate the flexibility or deformationcharacteristic for each cell, reference may be made to FIG. 2A of thedrawing, where an individual cell C is bounded by juncture lines 7 andwalls 5 and 6; however, when tensile forces T are exerted with respectto the walls of the cell in the direction indicated, there can bestraightening of the walls 5 into the partially flattened shapes 5 andthe displacement of juncture lines 7 into positionings 7 without causingjuncture lines 7 to move closer to one another. In other words, thecurved or arcuate walls 5 will tend to deform into a somewhat straighterconfiguration without necessarily causing immediate breakage to permitjuncture lines to shift somewhat and give overall flexibility to theunitary honeycomb structure. Actually, there is probably some rotationof the immediate juncture lines at 7 and 7' due to rigidity and momentforces that could cause some straightening of walls 6 and a slightspreading apart ofjunctures 7 and 7.

In FIG. 3 of the drawing, there is indicated what might be considered amodified hexagonal cell pattern where hexagonal cells, indicated by dashlines 8, are provided with alternating curved wall portions to result ina modified clover-leaf pattern. Specifically, each cell H has anopposing set of walls 9 that curve or bow in the same direction in anyone line of cells, another opposing set of walls 10 which also bow inthe same direction in their row, and a third set of opposing walls 11which bow in the same direction in their row. It will also be noted thatthere is the alternate bowing outwardly and inwardly with respect tonext adjacent walls around the periphery of the cell H, with one wall 9going outwardly and the next adjacent walls 10 and 11 bowing inwardlyor, conversely, where a wall 9 bows inwardly the next adjacent walls 10and 11 will bow outwardly. In this clover-leaf pattern, each cell H inany one row along any one of the three rows thereof, that are 120 apart,will have the same pattern or configuration.

It may be noted further with respect to FIG. 3 of the drawing, ascompared to the pattern in FIG. 2, that the three sets of opposing wallsfor any one cell will permit tensile forces to act along more than onedirection at the same time and that normally four wall sections will betending to flatten or straighten out under tensile forces and that fourjuncture lines may be displaced with respect to any one cell along thedirection of the tensile forces. Still further, juncture lines in atransverse direction to the tensile forces will not tend to move towardone another and will be maintained separate by rotational effects atjuncture lines and by the compressive resistance of the opposing wallswhich are extending generally transverse to the direction of the tensileforces. Again, the net result is that the curved wall portions canresist tensile forces by being deformed and flattened to some degreewhile at the same time permit juncture lines to move and be displacedwithin any one honeycomb structure in a manner so as to eliminatebreakage of individual wall members and a resulting failure to theoverall ceramic structure.

In FIG. 4 of the drawing there is indicated a manufacturing procedurewhen corrugated shaped partitioning members of green ceramic may beintermeshed at substantially right angles to one another to formintersecting and adjacent wall portions of a cell, and whereby aplurality of such members can result in a configuration similar to thatshown in FIG. 2 of the drawing. Specifically, a plurality of corrugatedform members, such as 12 with slots 13, can be made to fit egg cratefashion into a plurality of corrugated members, such as 14 having slots15, and at thereto to form a cellular type of structure. It is to berealized that any number of wall members 12 at desired spaced distanceswould be utilized in one direction to fit into the spaced slots 15 andthat another plurality of wall members 14 would be utilized at desiredparallel spaced distances from one another to fit into the slots 13 suchthat there is the intermeshing of the walls to result in theconfiguration of FIG. 2 with desired sized cells. A heating and curingoperation following the interlocking of members will result in thedesired sintering of the wall members to form tightly fused juncturelines between resulting parallel cells throughout the honeycombstructure.

In FIG. 5 of the drawing, there is indicated that a specially formedgreen sheet of ceramic material, such as 16, can be brought into contactwith a next adjacent specially formed sheet 17 at the arcuate zones 18to result in cell patterns H and that such system might well be utilizedto form a cellular structure with a multiplicity of cells H. The heatingand fusing of the juncture areas 18 will provide the sintering andwelding of all of the sheets into a resulting rigid structure.

Although the desired cell patterns and configurations may be obtained inaccordance with the procedures set forth in connection with thedescriptions of FIGS. 4 and 5, it is generally preferred that thedesired cell patterns be obtained by an extruding procedure whereaccurate uniform, thin wall partitions can be provided between themultiplicity of specially shaped cells in any one structure.

The size of the cells in a particular honeycomb structure, ashereinbefore noted, will typically be selected to be in accordance withpressure drop limitations for a particular stream being passed through ahoneycomb element, or through a series of elements. Typically, cellsizes may be from one thirty-second inch, or less, nominal diameter toone-half inch or more. It may also be noted that honeycomb elements maybe of varying shapes for a particular reactor chamber or housing andthat special shapes may be cut from larger honeycomb units producedunder any one form of manufacturing procedure.

The present forms or configurations of cellular structures may be madeto have varying coefficients of expansion depending upon the type ofceramic material utilized in manufacturing the skeletal honeycombmaterial. Typically, the coefficient of expansion for the honeycombstructure will be small as compared to steel or other metal housings andas a result a core element of the present invention may well be utilizedin metal housings without requiring a resilient expansion absorbingmedium between the external wall of the honeycomb structure and theinside wall of the housing. In other words, honeycomb materialsutilizing the present forms of configurations can have a certain degreeof flexibility within the housing without undergoing breakage problemswhen subjected to non-uniform temperature conditions.

I claim as my invention:

1. A ceramic composite with a multiplicity of parallel cells in ahoneycomb type of structure which can deform to accommodate compressionand tensile forces from non-uniform temperature conditions, whichcomprises, having all interconnecting walls between juncture lines ofthe walls and between adjacent cells being curved'and oriented one toanother in a reoccurring symmetrical pattern, each of said parallelcells being formed and defined by two sets of opposing curved walls, andwith one set of walls generally normal to the other in the overallpattern and at the junctures, said walls for any one cell being suchthat one set of opposing walls will bow towards one another and theother set will bow away from one another to form a necked-in anddumb-bell form of cross-sectional configuration,

and all cells having a common'wal] with an adjacent cell will be of thesame configuration as such cell except that it will be in an orientationof with respect thereto, whereby expansion movements in directionstransverse to the length of the longitudinal cells that are due todifferential temperature conditions can cause deformation andstraightening of one set of opposing curved walls without causingjuncture lines between cells to tend to move closer together in adirection generally transverse to the walls being straightened and tothereby provide a less fragile structure.

2. The ceramic composite structure claim 1 further characterized in thatsaid structure is provided with an active oxidizing catalyst coatingmaterial suitable to provide for the conversion of a noxious-gaseousstream.

3. A ceramic composite with a multiplicity of parallel cells in ahoneycomb type of structure which can deform to accommodate compressionand tensile forces from non-uniform temperature conditions, whichcomprises, having all interconnecting walls between juncture lines ofthe walls and between adjacent cells being curved and oriented one toanother in a reoccurring symmetrical pattern, each of said parallelcells being formed and defined by three sets of opposing curved walls,with each set of walls beingat approximately with respect to the nextadjacent set of walls to define any one cell, with next adjacent wallsaround an individual cell alternately bowing inwardly and outwardly,opposing curved partitioning walls between adjacent cells in any one rowthereof are bowed in the same direction, and each cell in any given rowof cells has the same cross-sectional configuration as the other cellsand is in the same orientation, whereby to readily provide tension anddeformation along any one of three axis without causing any substantialreduced spacing between juncture lines along either of the other 120transverse axes.

4. The ceramic composite structure of claim 3 further characterized inthat said structure is provided with an active oxidizing catalystcoating material suitable to provide for the conversion of a noxiousgaseous stream.

1. A CERAMIC COMPOSITE WITH A MULTIPLICITY OF PARALLEL CELLS IN AHONEYCOMB TYPE OF STRUCTURE WHICH CAN DEFORM TO ACCOMMODATE COMPRESSIONAND TENSILE FORCES FROM NON-UNIFORM TEMPERATURE CONDITIONS, WHICHCOMPRISES, HAVING ALL INTERCONNECTING WALLS BETWEEN JUNCTURE LINES OFTHE WALLS AND BETWEEN ADJACENT CELLS BEING CURVED AND ORIENTED ON TOANOTHER IN A REOCCURING SYMMETRICAL PATTERN, EACH OF SAID PARALLEL CELLSBEING FORMED AND DEFINED BY TWO SETS OF OPPOSING CURVED WALLS, AND WITHONE SET OF WALLS GENERALLY NORMAL TO THE OTHER IN THE OVERALL PATTERNAND AT THE JUNCTURES, SAID WALLS FOR ANY ONE CELL BEING SUCH THAT ONESET OF OPPOSING WALLS WILL BOW TOWARDS ONE OTHER AND THE OTHER SET WILLBOW AWAY FROM ONE ANOTHER TO FORM A NECKED-IN AND DUMB-BELL FORM OFCROSS-SECTIONAL CONFIGURATION, AND ALL CELLS HAVING A COMMON WALL WITHAN ADJACENT CELL WILL BE OF THE SAME CONFIGURATION AS SUCH CELL EXCEPTTHAT IT WILL BE IN AN ORIENTATION OF 90* WITH RESPECT THERETO, WHEREBYEXPANSION MOVEMENTS IN DIRECTIONS TRANSVERSE TO THE LENGTH OF THELONGTUDINAL CELL THAT ARE DUE TO DIFFERENTIAL TEMPERATURE CONDITIONS CANCAUSE DEFORMATION AND STRAIGHTENING OF ONE SET OF OPPOSING CURVED WALLSWITHOUT CAUSING JUNCTURE LINES BETWEEN CELLS TO TEND TO MOVE CLOSERTOGETHER IN A DIRECTION GENERALLY TRANSVERSE TO THE WALLS BEINGSTRAIGHTENED AND TO THEREBY PROVIDE A LESS FRAGILE STRUCTURE.
 2. Theceramic composite structure claim 1 further characterized in that saidstructure is provided with an active oxidizing catalyst coating materialsuitable to provide for the conversion of a noxious-gaseous stream.
 3. Aceramic composite with a multiplicity of parallel cells in a honeycombtype of structure which can deform to accommodate compression andtensile forces from non-uniform temperature conditions, which comprises,having all interconnecting walls between juncture lines of the walls andbetween adjacent cells being curved and oriented one to another in areoccurring symmetrical pattern, each of said parallel cells beingformed and defined by three sets of opposing curved walls, with each setof walls being at approximately 120* with respect to the next adjacentset of walls to define any one cell, with next adjacent walls around anindividual cell alternately bowing inwardly and outwardly, opposingcurved partitioning walls between adjacent cells in any one row thereofare bowed in the same direction, and each cell in any given row of cellshas the same cross-sectional configuration as the other cells and is inthe same orientation, whereby to readily provide tension and deformationalong any one of three axis without causing any substantial reducedspacing between juncture lines along either of the other 120* transverseaxes.
 4. The ceramic composite structure of claim 3 furthercharacterized in that said structure is provided with an activeoxidizing catalyst coating material suitable to provide for theconversion of a noxious gaseous stream.